This invention relates to incandescent lamps having enhanced light diffusion developed by an electrostatically coated inner surface of the outer envelope of the lamp cooperating with the outer surface of the outer envelope which is sandblasted except for the neck section of the incandescent lamp.
As is known, it has long been desired to produce a more diffused softer light output from an incandescent lamp developed by an incandescent filament. For example, it is desired to produce an apparently less distinct light output of the incandescent lamp or have it appear that the light output of the incandescent lamp is produced by a distributed light source.
Incandescent lamps for which a more diffused light output is particularly suited are those typically used by a consumer to accommodate reading applications such as the commonly termed three (3)-way lamp and relatively high wattage standard incandescent lamps in the range of about 150 watts to about 300 watts.
A technique for decreasing the apparent intensity of a filament is described in U.S. patent application Ser. No. 780,059 of Susan A. Blau, which is assigned to the same assignee of the present invention. The U.S. patent application Ser. No. 780,059 describes an incandescent lamp having an outer envelope with its inner surface coated with a relatively thick electrostatically deposited light-diffusion coating and substantially all of its outer surface sandblasted or chemically etched so that the combination of light-diffusion coating and sandblasting provides an enhanced light diffusion output of the incandescent lamp.
It has been determined that incandescent lamps of U.S. application Ser. No. 780,059 while serving their desired functions have a limitation with regard to some amount of the incandescent lamps experiencing a breakage at the region where the outer envelope is joined to the electrically conductive base of the lamp. This breakage problem is primarily encountered as in-process losses during the manufacturing of the lamps and are commonly termed infant mortality failures. Major factors to this undesirable breakage is that the sandblasting treatment and residual tension, both on the outer surface of the incandescent lamp, contribute to the breakage.
It is desired that the beneficial contributions of the sandblasted incandescent lamps of U.S. application Ser. No. 780,059 be preserved, but accomplish such sandblasting so as to significantly reduce or even eliminate the undesirable amount of infant mortality breakage experienced in the region of the joinder of the outer envelope to the electrically conductive base of the lamp.
Accordingly, it is an object of the present invention to provide incandescent lamps having diffused light output developed by a light-diffusion coating on the inner surface of the incandescent lamp along with a sandblasted outer surface of the lamp without causing or at least substantially eliminating the breakage experienced in the region of the joinder of the outer envelope to the electrically conductive base of the lamp.